Using robots to enhance lean manufacturing

Both large and small manufacturing operations can greatly benefit from the use of robots and, with Australia’s currently well-publicised manufacturing industry challenges, perhaps now is the time to consider the advantages of increased application of robotics.

Over the past three decades, robotics has made it possible for manufacturers to greatly increase the scale of factory automation. With over 160,000 sold each year*, industrial robots have become a mainstay of all sizes and types of manufacturing facilities, resulting in higher production rates, improved quality with decreased requirements for human intervention. Robots also elevate the nature of work by removing people from dull, dirty and dangerous tasks. As a result of greater efficiencies, robots and other forms of automation are rapidly becoming a core component of lean manufacturing and helping to reduce manufacturing costs.

Adding robotic automation, however, does not automatically make a manufacturing environment lean, but they are often integrated within the manufacturing process to support and enhance lean manufacturing systems. Success criteria for the use of robots to support lean are:

• Repeatability: robots improve product quality and consistency, and reduce waste.
• Speed: robots can help increase production and reduce wait time.
• Accuracy: robots help to reduce scrap.
• Flexibility: robots reduce training and changeover time - with a target of single-minute exchange of die (SMED), and often achieving one-touch exchange of die, (OTED) goals.

Figure 1: Coordination between multiple robots reduces cycle times and speeds production.

Lean systems and robots

No automation system or robotic solution is by its own nature lean. One thing that often gets overlooked is that automation systems (with or without robots) can actually speed up the creation of waste and reduce profitability if not designed into the system properly.

Designing the manufacturing system to be lean is one of the largest challenges faced by engineers today. A few of the factors which must be taken into account while designing a lean manufacturing system with robots are:

• Allowable scrap rate
• Conveyor and other transportation requirements
• Cycle time requirements by station or operation
• Equipment reliability and downtime statistics
• Flexibility required in the process
• Human machine interface requirements
• Line automation requirements (percentage automated versus manual)
• Line production rate requirement
• Product handling requirements
• Maintenance requirements
• Repair time of equipment
• Space available for robotic operations
• Safety standards and ergonomics guidelines
• Number of product variants

Traditional production lines are designed to be an effective collaboration between man and machine. While the machines (including robots) can be programmed for optimal performance, people cannot. Effective ‘lean’ robot cells must take this into account. An efficiently designed automated robotic station must take into account the human variable and not limit the stations ahead in the line by rigidly ensuring consistent system performance.

Most importantly, the decision to use robots must be justified by an ROI analysis. Small and large manufacturers have proven today’s robots can significantly improve the ROI in a manufacturing environment, especially when implementing robots in support of a lean initiative - but again, planning is critical. The robots must be properly incorporated into the overall lean manufacturing environment to get the desired results.

Figure 2: Robots elevate the nature of work by reducing large lifting requirements.

Machine tending and materials handling applications

Machine tending and materials handling used to be purely manual tasks. Operators would transport material from one fixture or machine to the next, wait on the equipment to finish its task, and then relocate the processed part to another tool or process fixture. In most cases, several operators were required. Today, these labour-intensive tasks are often accomplished using robots, especially in operations requiring high speed and accuracy.

Many applications, such as baked goods coming out of an oven on a conveyor, are picked and set into their packaging. Then, the individually packaged products are automatically placed into cases, ready to be palletised. The palletising robot can then place cases accurately on the pallet. Each of these robotic applications may be configured specifically for the customer the product is being shipped to. For example, different customers may have different packaging and palletising requirements than others. Each order can be picked, packaged and palletised automatically to meet the customer’s unique requirements.

So, how do robots make a handling system lean?

1. There is no wait time for operators. A materials handling robot can be set up to multi-task, performing additional processing operations between other operations.
2. Robots have negligible downtime. Robots deliver a limited production loss compared to manual operations, which tend to be error prone and inconsistent in terms of production rate, shifts, work breaks, etc.
3. Robots are less expensive to operate, compared to human labour - especially when overtime is required. The ROI can be quickly realised when there is high demand for the manufactured product.
4. Robots are capable of highly accurate, highly repeatable tasks, which results in fewer scrap parts once the robot tasks are optimised.
5. Robots do not get fatigued and are not affected by heat, dust, humidity and other challenging work environments.

Figure 3: An example of robots working in coordination - and removing and deburring parts, then spraying the dies to prepare for the next drop - removing humans from a high-temperature environment.

Application flexibility

To incorporate robots into a lean manufacturing environment, engineers should look to process as many operations as possible within the given floor space.

Today’s robots can incorporate tool changers to allow the robot to handle more than one task. With one robot now able to perform multiple functions, the manufacturer will see improved utilisation, and has the ability to create a leaner manufacturing environment overall. In the die cast industry for example, robots are commonly used for parts handling as well as finishing operations like deburring and grinding. Robots in an automotive body shop are often used for material handling of parts as well as welding or sealant application.

Robots that need to perform more than one function are built with tool-changing equipment that allow robots to disengage/engage new end-effector tooling.

Advances in robotics have given engineers the flexibility they need to incorporate robotics into a lean manufacturing initiative. Robots have furthered the ability to optimise operations based on floor space, cycle time and feasibility constraints. Over time, multi-arm robots will become the norm, continuing the progression of manufacturing operations that are faster and leaner.

Robots and vision applications

Vision technology and robots are a natural pairing, and the combination has resulted in robotic operations that are leaner than ever before. Vision systems are commonly used to allow robots to vary their motion targets based on vision-generated guidance information.

Operations that require making visual distinctions and decisions (such as racking/unracking of parts, part picking from bins and part inspections) were once exclusively handled by human operators. By combining robotics with vision-guided systems, these same tasks can be performed by robots with higher consistency, accuracy, repeatability and speed. Vision-equipped robots can also reduce imperfections and scrap material in finishing operations such as routing, grinding and sealing.

In the inspection arena, robots are used heavily in flexible measurement systems (FMS). Robots mounted with vision cameras can collect information from multiple locations, dramatically reducing the number of vision cameras and fixtures required to inspect parts.

Using vision-equipped robots, lean manufacturing environments can be significantly improved, especially in areas where the movement, flexibility and simple decision-making of the human operator was once required.

Coordinated motion and cooperative applications

In a coordinated motion system, two or more robots are controlled by a single controller. The controller allows for communication between robots to simultaneously perform coordinated operations on a single large part.

Coordinating robot movements can significantly reduce the time wasted in the manufacturing process. For example, roof assembly in the automotive industry is now commonly performed with one robot firmly gripping the automobile roof, while other robots weld and assemble the roof to the main auto body. Robots are also used for parts transfer between assembly stations instead of transfer equipment like lift-and-carry systems or shuttles.

Figure 4: Two robots used to load, unload and weld parts with little human intervention and with a high degree of accuracy.

Improved cycle time

Many food packaging applications are performed by an operator (or team of operators) manually picking and packaging the products. This adds costs, can be physically demanding and may create the potential for product contamination. Often fixed automation is used, but this can severely reduce the flexibility of the application. When product marketing develops a new product or a customer demands a new package size or type, the fixed automation is often too inflexible to cost-effectively deal with the change. Robots have become a powerful tool in the automation of pick-and-place applications such as pancakes, sausages, muffins and many other packaged or pre-packaged foods, for example.

In major manufacturing assembly plants, there are often hundreds of robots performing materials handling, machine tending, welding, finishing, painting and other assembly operations. Wasted robot motion can cause cycle-time issues, creating bottlenecks and loss of production. Poor path planning can cause product quality issues that can lead to scrap parts. The cost of lost production is a major drain on overall corporate profitability. Ensuring that the cycle time for robotic work cells is optimised is very important to the lean manufacturing plan.

Some of the common cycle-time issues impacting lean manufacturing are:

• Lack of parts available to robots, causing delays in production
• Unsafe work conditions, causing slow human operation in situations where robots and humans work in a cooperative environment
• Poor equipment design, resulting in wasted repair efforts
• Bottlenecked stations, causing part blocking or starvation at other stations
• Individual robots over-cycle, causing an entire work cell to be over-cycle
• Wait times on other equipment, causing robots to go over-cycle
• Poor processing, resulting in work overload on robots, operators or machines
• Poor human machine interface, causing delays in manufacturing
• Poor software and controls engineering, resulting in inefficient I/O and communication between equipment

Detailed planning of robotic operations prior to system integration can go a long way towards controlling equipment and labour costs.

Workplace safety

Most manufacturing operations have a degree of human injury risk. One of the primary reasons to automate a process using robots is to improve workplace safety. High-risk tasks like unloading parts from a fast-moving press or working with molten metal are definitely not tasks suited for human operators. In these cases, robots are invaluable in lowering the risk of injury or death.

An unsafe workplace leads to fear-driven human inefficiency, lowered production rates, higher insurance costs, and high employee turnover. Conversely, a safe workplace boosts morale, increases employee retention and lowers costs, which ultimately improves the bottom line. And again, robots can significantly elevate the nature of work by removing people from dull, dirty and dangerous tasks.

Figure 5: Robots speed up the palletising of heavy objects while reducing waste and the concern of a worker being hurt.

Robots can make the work environment safer by performing functions that are unsafe for humans, but robots themselves can also be unsafe. For example, if a robot cell is not guarded properly, operators may take longer to service the station because of fear of injury. Whenever robots are used, the environment must be carefully analysed and proper protocols instituted to keep the work cell safe. If the employees don’t feel safe, the robotics implementation will not be as lean as designed.

Many applications require the strengths of both people and robots but, until recently, this could be very dangerous. Now specialised software can allow robots and operators to collaborate much more closely without compromising on safety. This combines the flexibility of human interaction with the precision and handling capacity of robots to make applications lean, accurate and very safe for operators.

Conclusion

Robots, if used correctly, can enhance a lean manufacturing environment. Robots offer speed and accuracy that can’t be achieved with human labour alone. Robots can also reduce operating costs, reduce scrap and are flexible for future changes. Few other manufacturing solutions can reduce waste as well as robots when designed into the system properly.

Robotics capabilities have only increased with time, while costs have continued to fall. Major robot manufacturers are constantly upgrading their robots with increased payload capacity, greater accuracy, increased reach and range of motion, improved speed and acceleration, faster communication with external equipment, better safety features and lower operational costs.

If you have not explored incorporating robotics into your manufacturing environment lately, it is probably time to take another look. With a lower cost, more capabilities and a large number of successful manufacturing implementations, robots can increase your return, improve quality, reduce costs and help you eliminate waste.

* As reported in the World Robotics 2013 - Industrial Robots report and previously on ProcessOnline.